Whats the best thermal paste for a CPU?

Eximo

Titan
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Depends on the cooler you intend to apply.

Direct contact heat pipes tend to need more thermal compound to fill gaps between them, more paste like compounds work best here. Machined surfaces have many small grooves that need filling, so slightly more fluid (lower viscosity) work better for these. A plated surface is extremely smooth, so very little paste is needed. This is when you want something that is extremenly thermally conductive and with a quite low viscosity. Some of the high end 'nano-diamond' products are worthwhile.

Also the liquid metal ones, but they are somewhat dangerous to use...